1. Field of the Invention
The present invention relates to catheters used for surgical operations, and more specifically, to fiber optic catheters used for illuminating and ablating intravascular regions and means for terminating such catheters.
2. Description of the Related Art
Fiber optic catheters have been constructed in which hollow tubular devices, or catheters, containing optical fibers, are inserted into veins or arteries. Radiant energy is conducted along the fibers to illuminate internal parts of the body for diagnostic and surgical purposes. There are many medical applications in which it is desirable to deliver energy, such as laser energy, through an optical fiber or similar waveguide device disposed in a body cavity for treatment or diagnosis. These include the ablation of tissue such as plaque and tumors, the destruction of calculi and the heating of bleeding vessels for coagulation. The lasers used may produce either pulsed or continuous-wave light of wavelengths ranging from the ultra-violet to the infra-red.
Fiber optic catheters have been employed to generate heat at the distal end of the catheter as the mechanism of operation. One known system employs laser radiation for heating a metal tip on the end of the fiber so that the heated tip burns through the plaque obstructing the vessel. This is disadvantageous in that the tip may burn through the wall of the vessel. Moreover, the location and degree of burning cannot be precisely controlled using this type of tip, and tissue from the vessel wall may stick to the hot tip. As a result, the tissue tears as the tip is moved, producing a thrombosis. The heated metal tip also requires mechanical pressure to force the tip through the plaque, and is not very successful with blockages located at any substantial distance from the entry point of the catheter, or in small winding cardiac arteries, since sufficient mechanical pressure cannot be exerted on the tip to force it through the plaque.
In another proposed solution a sapphire tip, through which energy passes to the surrounding tissue, has been used. The surface of a highly polished sapphire is difficult to bond to a glass fiber, and accordingly secure junctions between optical fibers and sapphire cannot be produced. For this reason the sapphire is mounted on a metal connector fixed to a catheter through which the fiber is passed. Such a device is thick and relatively inflexible, making it unsuitable for use in small blood vessels or where it is required to pass a balloon catheter over it. Also, it is difficult to maintain the position of the fiber with respect to the sapphire, and the junction becomes contaminated with charred blood. Since the refractive index of sapphire is higher than that of the fiber, there is a heat loss at the sapphire-fiber interface and the metal tip becomes heated, thus introducing the disadvantages mentioned above.
U.S. Pat. No. 4,860,743 and U.S. Pat. No. 5,041,109 to Abela disclose a tip for a laser catheter based on a combination of the metal tip/sapphire lens concepts where sapphire spherical lenses on the tip are used to deliver some laser energy directly to an area being ablated, while some of the energy is used to heat the metal tip. In this way, plaque blocking the vessel is vaporized to allow the catheter to be moved farther into the vessel, while the remaining obstructive tissue is burned away.
Ball-tipped or lens-tipped devices have been proposed, and these can be readily formed merely by melting the tip of a silica-glass optical fiber. There are, however, problems with respect to the mechanical strength and safety for such tips, particularly after exposure to heat, laser light and the mechanical stresses of clinical uses. A supporting structure, for example a metal collar, can be employed with such tips, but this arrangement becomes heated in use, again with the disadvantages mentioned above.
U.S. Pat. No. 4,967,745 to Hayes et al., U.S. Pat. No. 5,032,123 to Katz et al., and U.S. Pat. No. 5,034,010 to Kittrell et al. disclose laser catheters having a transparent shield over the distal end of the optical fibers. A similar design is disclosed in U.S. Pat. No. 5,041,108 to Fox et al., which uses individual lenses for each optical fiber to focus the laser beam onto the area to be illuminated.
All of the above fiber optic catheter tips are disadvantageous in that they require great effort and care to fabricate. For instance, in many cases, the tips must be machined with individual channels for the optical fibers. In such a case, the channels must be precision machined to ensure their concentric placement about the catheter tip for even light distribution. Also, the relatively complex shapes of the above-mentioned tips do not allow for the precise machining of the tip surfaces at desired angles and dimensions.
After the tip is fabricated, a great deal of effort is required to properly assemble the individual components into a device that will withstand normal field use and perform as expected. For instance, it is desirable to glue the tip onto the laser catheter to secure it for normal field use. In this case, it is difficult to accurately control the wicking action of the glue along the optical fibers when using one of the aforementioned tips.